(a) Field of the Invention
This invention relates to a standard zoom lens system comprising two lens groups and having a large aperture ratio, in which the angle of view varies from about 35.degree. to 60.degree..
(b) Description of the Prior Art
Zoom lens systems comprising two lens groups have been known. However, in a compact zoom lens system having a small F-number, spherical aberration caused by zooming is large and this aberration is not balanced with other aberrations, so that a desired performance cannot be obtained. In order to improve the performance it is necessary to increase the number of lenses, which means enlargement in size and is against the requirement for compactness of a lens system.
Known zoom lens systems comprising two lens groups similar to the zoom lens system according to the present invention are disclosed in Japanese Published Unexamined Patent Application No. 153752/77 and Japanese Published Unexamined Patent Application No. 60717/83. The lens system disclosed in the former has a small aperture ratio and that disclosed in the latter has a large number of lenses and a complex configuration, so that the system is not compact.